Closed-cell polyurethane foams are widely used for insulation purposes in building construction and in the manufacture of energy efficient electrical appliances. In the construction industry, polyurethane (polyisocyanurate) board stock is used in roofing and siding for its insulation and load-carrying capabilities. Poured and sprayed polyurethane foams are also used in construction. Sprayed polyurethane foams are widely used for insulating large structures such as storage tanks, etc. Pour-in-place polyurethane foams are used, for example, in appliances such as refrigerators and freezers plus they are used in making refrigerated trucks and railcars.
All of these various types of polyurethane foams require expansion agents (blowing agents) for their manufacture. Insulating foams depend on the use of halocarbon blowing agents, not only to foam the polymer but, more importantly, for their low thermal vapor conductivity. This property, vapor conductivity, contributes significantly to the foam's insulation value. Historically, these polyurethane foams have been made using trichlorofluoromethane (CFC-11) as the primary blowing agent.
A second important type of insulating foam is the phenolic foam. This foam, which displays very attractive non-flammability characteristics, is generally made With CFC-11 and CFC-113 (1,1,2-trichloro-1,2,2-trifluoroethane) blowing agents.
CFC-11, historically the blowing agent of choice in producing polyurethane/polyisocyanurate foams, is being phased out because of its effect on the environment.
In September 1987, the United Nations through its Environment Program (UNEP) issued a proposal calling for a 50 percent reduction in worldwide production of fully halogenated chlorofluorocarbons (HCFCs) by 1998. This proposal was ratified Jan. 1, 1989 and became effective Jul. 1, 1989. On Nov. 15, 1990, the U.S. Clean Air Act was amended in such a manner as to provide for a production freeze and use limitation to refrigeration for HCFCs (e.g., HCFC-22) on Jan. 1, 2015. Complete production ban on HCFCs is scheduled for Jan. 1, 2030. This phase-out of HCFCs by 2030 adds incentive to develop an HFC alternative for manufacturing polyurethane/polyisocyanurate foam. There is, therefore, a need for an effective blowing composition for polyurethane foams that contributes little or nothing to the stratosphere ozone depletion process or to the "greenhouse effect"
The blowing agent should also provide a relatively low thermal conductivity to the foam, i.e., provide relatively high insulation values for the foam. There are three primary factors to cause heat to be lost or transferred across or through an insulating foam: (1) conductivity through the foam cell gas, (2) conductivity through the solid polymer and (3) radiational heat loss across the foam cells. The contribution of these factors to total heat loss is (1) about 44 percent, (2) about 22 percent and (3) about 34 percent. Of these three, the blowing agent contributes significantly only to the thermal conductivity through the foam cell gas.
A fourth factor contributing to the insulation value is the size of the cells formed during the foaming process. The blowing agent should be capable of contributing to the formation of a uniform, closed-cell structure will small, fine cells.
The basic object of this invention is to provide an improved, efficient process for producing polyurethane and polyisocyanurate foams employing an effective blowing agent that has substantially no ozone depletion potential (ODP), has no or very low global warming potential (GWP), i.e. makes no significant contribution to the "greenhouse effect", and provides foams that display relatively high insulation values.